Micheel, who reached 7 under par on the back nine, posted a 1-under 69, his third consecutive round under 70. Campbell carded the lowest round of the championship with a 5-under 65 and the pair are tied at 4-under-par 206.
Micheel reached 7 under par after a three-foot birdie at the par-3 15th but things went downhill quickly for the second-round leader. He drove into the right rough at 16 and had no other play but to pitch out to the fairway. Micheel's third landed 35 feet from the hole but his par save missed the hole.
At the 17th, Micheel missed the short grass again off the tee and played his second into a greenside bunker. His blast from the trap came up 40 feet short and once again he was unable to convert on the long par save.
Micheel, now with a one-stroke lead over Campbell, drove into the right rough near a bunker. He laid up short of the putting surface with his second and knocked his third 20 feet left of the pin. His putt for par came up left and short and so it was a share of the third-round lead instead of sitting on the lead by himself overnight.
'If you miss the fairway it doesn't matter if it's hole No. 1 or hole No. 16, 17 or 18, you're probably going to make bogey,' said Micheel. 'Overall, I'll be okay tonight. It's not a problem.'
While Micheel limped into the clubhouse, Campbell made his move up the leaderboard at the end of the round. Campbell hit a 6-iron to 15 feet to set up birdie at the 15th and the 29-year-old made it two in a row with a kick-in birdie at No. 16.
Campbell ran into trouble at the 17th when his drive went right, hit a tree and kept going right. He pitched out to the fairway, then hit a 7-iron to the middle of the green. Campbell two-putted for bogey but at 18 he sank a 35-footer for birdie to polish off his round of 65.
'The putt on 18 made up for all of the ones I missed all day,' said Campbell. 'Today I felt really good out there. I hit a lot of fairways and a lot of greens and gave myself a lot of opportunities for birdie.'
Masters champion Mike Weir shot an even-par 70 on Saturday and is alone in third place at 1-under-par 209. South African Tim Clark shot a 2-under 68 on Saturday and is alone in fourth place at even-par 210.
With two relative unknowns like Micheel and Campbell, both Nationwide Tour graduates, atop the leaderboard, some big names were unable to make a charge into the lead.
Phil Mickelson, the first-round co-leader, put together a round of 2-over 72 and is part of a group tied for 12th at 3-over-par 213.
Tiger Woods, still in search of his first major title since the 2002 U.S. Open at Bethpage, carded a third-round 73 and is tied for 43rd place at 9-over-par 219.
'I played my tail off to shoot 3 over today. I really did,' said Woods, who the Wanamaker Trophy in both 1999 and 2000. 'I grinded my butt off just to shoot 3 over.'
Things don't look good for Woods, barring a miraculous round on Sunday, and 2003 looks like it will be the first season without a major since 1998.
As shocking as Woods not having a major trophy this year, it might be even stranger to see who has won the big four of golf. Weir and Jim Furyk, who won the U.S. Open at Olympia Fields, were top players when they won their inaugural majors but British Open champ Ben Curtis was ranked nearly 400th in the world when he titled at Royal St. Georges.
Now it looks like Micheel or Campbell are ready to add their name to the list. Twelve of the last 15 PGA Champions were first-time major winners and if one of these two, or any other majorless player, can visit the winner's circle Sunday afternoon, it will be the first time since 1969 that all four major winners were first-timers.
'I will say it will probably enter my mind,' said Campbell. 'I've tried to keep it out of my mind but it's kind of inevitable that it will happen. We've still got a lot of golf to play, 18 holes tomorrow. I just want to come out and try to stay focused on what I'm doing and not try to get ahead of myself.'
Campbell opened with four consecutive pars but broke into red figures with a tap-in birdie at the fifth. He knocked a 3-iron to tap-in range for birdie at the seventh and made it two in a row with a 15-footer at No. 8.
He parred his next six holes before his dramatic finish that jumped him to the top of the leaderboard.
Micheel was in the final group Saturday and maybe nerves took over at No. 1 because the 34-year-old drove into the rough and made bogey. He settled down with five pars in a row, never really giving himself good looks at birdie.
Micheel drained back-to-back seven-footers for birdie at seven and eight and ran home a 30-footer for birdie at nine to make it three in a row.
On the second nine, Micheel made a 15-foot birdie putt at 12 to go to 6 under and along the way, he made some spectacular par saves. He sailed over the green at 13 but holed the 20-footer for the save.
He seemed to have the tournament wrapped up when he got to 7 under at 15, but Oak Hill's demanding closing holes caught up with him. Now he's in the final group on Sunday at a major championship, tied for the lead.
'Anybody can win,' said Micheel. 'If you're playing on the PGA Tour you can obviously play. Just because people haven't heard of me or Chad doesn't mean we can't play.'
Ernie Els (70), Billy Andrade (72), Briny Baird (67) and Alex Cejka (68) share fifth place at 1-over-par 211. Vijay Singh, the 1998 champion, Fred Funk and Charles Howell III all posted matching rounds of even-par 70 to tie for ninth at plus-2.